Nano rolling embossing and alignment is potential for future manufacturing. Related reports have been published in journals. Due to considerable optical power consumption in the liquid crystal display structure with efficiency of only 3%-6%. For the most power consumptive films such as polarizer films (60% of loss), color filters (70% of loss) and the aperture ratio issue (30% of loss), nano structured films has been reported using beam splitting by diffractive optical films to overcome the aforesaid issues concerning high power consumption and low efficiency. As shown in FIG. 1, the light from a light source 10 is emitted onto a beam splitting film 12 to be converged and then is transmitted onto a dichroic filter 14 for color separation. The diffractive optical films are manufactured by rolling embossing. Even though rolling embossing is less costly with higher throughput, the manufactured products are far from satisfactory due to mismatch of double-layered microstructures during alignment. For example, angle mismatch is one of the problems resulting from rolling embossing. When angle mismatch happens, beam splitting results in poor uniformity of polarized light distribution. When there is a small angle between the top and bottom gratings, the change in diffractivity leads to poor beam splitting. As a result, the information concerning mismatch between the double-layered microstructures has to be fed back to film driving mechanism so as to achieve nano-scale alignment by repeated corrections to improve the manufacturing yield and optical efficiency of the optical films.
The beam splitter has a grating structure, which can be manufactured by hot embossing or UV embossing. As shown in FIG. 2, a top roller 22 and a bottom roller 24 are provided with blazed grating patterns 220 and 240, respectively. The microstructured patterns on the rollers 22 and 24 can be transferred onto the optical film 20, which leads to an issue of finding the mismatch and the change in diffractivity as the optical film 20 is double-sided with high-precision alignment.
U.S. Pat. No. 7,121,496 discloses a method and a system for correcting web deformation during a roll-to-roll process, which uses a computer system to control the sensors and the substrate. However, this patent fails to achieve second-scale precision on transparent materials.
As trying to realize the effects of misalignment of a double-layered film by experiments, it is found that the signals concerning the layers cannot be both obtained at the same time using microscopy and that the change in the angle between the layers cannot be identified because the thickness of the thin film is about 0.4 mm and the grating has a period of 4 μm and depth of 1 μm. To observe the surface patterns, a high-magnification objective lens is required. However, such a high-magnification objective lens exhibits a short depth of focus so that the bottom grating cannot be observed. As a result, the alignment pattern with Morie' effect cannot be achieved. On the other hand, a low-magnification objective lens exhibits a small numerical aperture. The transparent optical film exhibits low-contrast patterns. Therefore, it has become an important issue to identify and detect the pattern difference without being affected by the environmental vibration.